Centrifugal pumps for liquids



Nov. 5, 1968 R. RIMMER 3,408,943

CENTRIFUGAL PUMPS FOR LIQUIDS Filed Aug. 22, 1966 FIG. 4.

lNvEN'roR TON/H Wmrmzza BY M AZ-W ATTQRNE United States Patent 3,408,943 CENTRIFUGAL PUMPS FOR LIQUIDS Ronald Rimmer, Churchdown, England, assignor to Dowty Fuel Systems Limited, Cheltenham, England, a British company Filed Aug. 22, 1966, Ser. No. 573,992 Claims priority, application Great Britain, Aug. 31, 1965, 37,123/65, 37,124/65 8 Claims. (Cl. 103-97) ABSTRACT OF THE DISCLOSURE A flow regulating mechanism is disclosed for a liquid supply system of the type wherein a hydraulic load is fed by a centrifugal pump having the inlet and outlet thereof adjacent the axis and the periphery of the pump chamber, respectively, and an operating speed at which its delivery rate exceeds the upper limit of the range of flow rates over which the demand may vary, so that the liquid flowthrough in the chamber assumes the form of an annulus in the relatively peripheral portion thereof, the relatively axial portion of the chamber being closed to atmosphere so that a hollow core is formed centrally of the liquid annulus to enable it to compensate for variation in the load at a particular demand by adjusting its radial depth. The flow regulating mechanism comprises a source of low pressure liquid which communicates with the pump inlet through a connection having a passage therein for regulating the pump inflow. The passage has an orifice opening thereinto, at one peripheral boundary of the inflow, and control means are connected to the passage to discharge a variable amount of additional liquid into the inflow, through the orifice, to generate a pressure change in the inflow which is variable over a range corresponding to the range of inflow rates needed to satisfy the demand.

This invention relates to pumping apparatus for liquids, of the kind in which the delivery of 'a centrifugal pump is controlled by regulating the supply of liquid to the eye of the pump impeller so that the liquid entering the pump and rotated by the pump impeller assumes a generally annular form within the radially outer part of the pump casing.

According to the invention, pumping apparatus for liquids comprises a centrifugal pump having a pump casing and an impeller rotatable therein, a flow regulating device connected between a low pressure liquid source and the pump inlet said regulating device having a main passage including a vortex chamber with a central discharge opening therefrom which forms the pump inlet, said regulating device having also at least one control orifice which is connected to a source of control liquid and which enters the main passage in a generally tangential direction, control means operable to vary the flow of liquid through the control orifice and thus to vary the angular velocity of the combined liquid streams at the periphery of the vortex chamber, the vortex chamber being so arranged that the rate at which liquid enters the pump through the discharge opening varies in inverse relation to the angular velocity, and 'a hydraulic load connected to the pump delivery, the load being such that, during operation of the pump, the liquid entering the pump and rotated by the impeller assumes a generally annular form within the radially outer part of the pump casing.

The main passage of the flow regulating device may include an annular passage leading into the vortex chamber, the annular passage and the vortex chamber having a common circumferential outer wall through which the control orifice opens substantially tangentially.

The source of control liquid may be provided by a con nection to the delivery of the pump whereby the net delivice ery of liquid to the hydraulic load is substantially equal to the flow from the low pressure source. The control flow is therefore independent of the net delivery since it is circulated in a closed loop which has one connection downstream of the low pressure source and .another connection upstream of the hydraulic load.

In the accompanying drawings FIGURE 1 shows as one embodiment of the invention, pumping apparatus suitable for supplying liquid fuel to the burners of an internal combustion gas turbine engine,

FIGURE 2 shows another embodiment of the invention, forming a modification of FIGURE 1,

FIGURE 3 is a section on the line III-1H of FIG- URE 1, and

FIGURE 4 is a section on the line IVIV of FIG- URE l.

A centrifugal pump 11, shown diagrammatically in FIGURE 1, has a casing 12 in which a drive shaft 13 and impeller 14 are mounted. The impeller has an eye 15 at the radial inward limit of the impeller blades, and a circular inlet opening 16 on the rotational axis of the impeller adjacent the eye 15. The opening 16 forms the discharge opening of a flow regulating device 17 which is secured to the pump casing 12. The regulating device comprises a housing in two parts 18, 19 having a common cylindrical bore 21 providing a main passage for liquid to flow through the device. The housing part 18 has a central inlet conduit 22 on the axis of the bore 21, which is connected through a servo device 23 to a boost pump 24 forming a low pressure liquid source. A cylindrical plug 25 has a flanged base 26 which is located and clamped between the housing parts 18, 19 by "a number of bolt fastenings 27. The cylindrical surface of the plug 25 is uniformly spaced from the bore 21 to provide an annular portion of the main passage 28 into which liquid from the conduit 22 can enter through arcuate openings 29 in the fi-anged base 26.

A baflle 31 in which the opening 16 is formed, is spaced from the downstream end of the plug 25 to form a vortex chamber 32. The opening 16 is flared on the discharge side to provide for a smooth fiow of liquid into the eye 15 of the impeller 14. A control orifice 33, FIGURE 4, formed in the housing part 19, opens tangentially into the annular passage 28. The inlet to the control orifice 33 is connected to the pump delivery conduit 34 by a pipe 35 which has a fixed restrictor 36 therein. A branch pipe 37 leads to a control valve in the servo device 23. The control valve comprises a nozzle 38 and a movable closure 39 which is formed by a lever pivoted at 41 in the servo device. Movement of the lever is controlled in part by a demand signal which is applied by two resilient bellows 42, 43 acting oppositely at the other end of the lever 39. The pressure in the bellows 42 is supplied from the delivery side of the engine compressor by way of a fixed restrictor 40 and a pipe 44. The pressure is variable :by a control lever 45 which is movable to vary the opening of a vent valve 46 connected to the pipe 44. The bellows 43 is supplied by the jet pipe pressure of the engine. A flowmeasuring device is provided by a tapered plug 47 which is movable with respect to the end of the bore 48 in a liquid inlet 49 to the servo device. The tapered plug 47 is loaded towards the bore 48 by a spring 51 which is seated against the lever 39 on the opposite side thereof from the nozzle 38. The position of the tapered plug 47 is a function of the flow through the inlet 49, and the spring 51 therefore applies .a force signal of flow on the lever 39 in the negative feedback sense.

The delivery conduit 34 leads to a burner gallery of the engine, shown symbolically by a burner nozzle 53, which provides a hydraulic load maintaining pressure at the delivery of the pump 11.

The operation of the regulating device will now be described. If there is no flow of control liquid through the tangential orifice 33, liquid entering the device 17 from the low pressure source 24 will flow through the annular passage 28 without any rotation about the central axis, and continue as a radially inwardly converging flow in the vortex chamber 32 to be discharbed through the opening 16 into the eye of the impeller 11. The regulating device 17 then offers minimum resistance to the flow of liquid through it.

If, on the other hand, there is a flow of control liquid through the orifice 33, rotation is imparted to the liquid flowing through the annular passage, whereby the combined liquid stream at the periphery of the vortex chamber 32 has an angular velocity which varies in accordance with the control flow. The rotation of the combined liquid stream in the vortex chamber 32 increases in angular velocity towards the centre, and this rotation creates a pressure dilference between the bore 21 and the opening 16 which increases the effective resistance to flow from the low pressure source. The rate at which liquid enters the pump is therefore inversely proportional to the angular velocity.

The centrifugal pump is designed to operate as a vapour core pump, that is to say the liquid entering the pump and rotated by the impeller assumes a generally annular form within the radially outer part of the pump casing 12. The regulating device 17 determines the rate at which liquid enters the pump, while the radial depth of the liquid annulus in the pump is self-adjusting at any given rotational speed of the pump impeller 14 to provide the delivery pressure at which the hydraulic load on the pump delivery will accept the liquid flow rate.

The operation of the pumping apparatus will now be described At any instant, the lever 39 of the servo device 23 is balanced under the opposed forces of the bellows 42, 43 at one end and under the opposed forces of the spring 51 and of pressure in the nozzle 38 at the other end. The pressure in the nozzle 38 determines the control flow through the tangential orifice 33 whereby the resulting rotation of the combined liquid stream in the vortex chamber 32 creates an effective resistance to liquid flow through the control device 17 as described.

The resulting flow from the source 24 is stabilised by the flow-measuring device 47, 48, for if there is an increase, the tapered plug 47 applies an increased spring load on the lever 39 to close the nozzle 38, thereby increasing the control flow through the orifice 33 .and thus the effective resistance of the control device 17. Conversely, a decrease of flow causes a reduction of effective resistance. Moreover, any increase in the delivery of the pump increases effective resistance of the regulating device 17.

The lever 45 provides a control for varying the flow to the pump 11. If it is turned clockwise to increase the restriction of the vent valve 46, the resulting pressure rise in the bellows 42 acts through the lever 39 to decrease the pressure in the nozzle 38. The flow through the tangential orifice 33 is decreased so that the pumping apparatus will stabilise at an increased flow rate. A decrease in resistance of the vent valve 46 conversely produces a reduced flow rate.

The pumping apparatus is preferably designed so that even at maximum flow, there is sufficient flow through the tangential orifice 33 to produce rotation of the combined stream in the vortex chamber 32 at a small angular velocity, though the rotation is not suflicient to produce any substantial effective resistance to flow. Thus over the operating range of the pumping apparatus, in which both the pump speed and fiow may be varied, the liquid flows through the orifice 16 into the eye 15 with a swirling motion which tends to give an even distribution of liquid around the rotational axis of the impeller 14. The swirling motion may either be in the same direction, or contrary to, the rotation of the impeller. Except possibly at higher flow rates, the vapour core extends centrally 4 1. 1 from th eye 15 and within the swirling discharge up to the transverse end "of the cylinder plug 25.

The liquid which flows through the tangential orifice 33 and through the control nozzle 38 is drawn from the pump delivery conduit 34, 'but it is returned to the flow from the low pressure source 24 downstream of the flowmeasuring device 47, J8, and combines with it before entering the pump. The'net delivery of high pressure liquid to the burner gallery 52 is therefore substantially equal to measure the flow of liquid from the low pressure source. The fact that the control flow through the orifice 33 is large when the net delivery is small, is therefore no disadvantage in providing a wide range of flow control because the control flow is independent of the net delivery. v t

In the embodiment described, the tapered plug 47 applies a direct load on the lever 39 through the spring 51. FIGURE 2 shows a modification in which the spring 51 is seated against'the interior of the 'servo device 23, while the tapered plug 47 co-operates with an orifice 48 in the wall 53 of an inlet chamber 54. The pressure in the inlet chamber 54 acts through another orifice 55 in the wall 53 against the underside of a diaphragm 56, while the pressure on the downstream side of the orifice 48 acts against the upper side of the diaphragm, the latter having a central stem 57 acting against the lever 39. The diaphragm 56 provides an amplified load signal compared with the load in the spring 51 and it is therefore more sensitive at low flow rates. The diaphragm enables the flow-measuring device 47, 48 to be designed for smaller pressure differences across it than in the embodiment of FIGURE 1.

It is possible, if desired, to impart a certain amount of prerotation to the liquid stream through the annular passage 28 in advance of the control orifice 33 by means of swirl vanes set at a suitable angle. Such swirl vanes may take the place of the supporting portions of the flange 26 which extend radialy-inwardly at the ends of the arcuate gaps 29. I

To provide an additional control for shuting down net pump delivery, a shut-off cock may be provided in the branch pipe 37. Alternatively, additional tangential orifices opening into the annular portion of the main passage 28 may be connectable with a source of shut-down control liquid.

An alternative embodiment of the pumping apparatus may have a servo device provided with a flow-measuring device in the delivery conduit 34 beyond the connections of the pipe 35.

The hydraulic load supplied by the delivery conduit 34 may, if desired, include alternative or additional means to determine the relationship of delivery pressure and net flow.

I claim as my invention: I

1. Pumping apparatus for liquids comprising a centrifugal pump having a pump casing and an impeller rotatable therein, a flow regulator device connected between a low pressure liquid source and the pump inlet, said regulator device having a main passage including a vortex chamber with a central discharge opening therefrom which forms the pump inlet, said regulator device having also at least one control orifice which is connected to a source of control liquid and which enters the main passage in a generally tangential direction, control means operable to vary the fiow of liquid through the control orifice and thus to vary the angular velocity of the combined liquid streams at the periphery of the vortex chambers, the vortex chamber being so arranged that the rate at which liquid enters the pump through the discharge varies in inverse relation to the angular velocity, a hydraulic load connected to the pump delivery, the load being such that, during operation of the pump, the liquid entering the pump and rotated by the impeller assumes a generally annular form within the radially outer part of the pump casing, and the main passage including an annular passage leading into the vortex chamber, the annular passage and the vortex chamber having a common circumferentially outer wall through which the control orifice opens substantially tangentially.

2. Pumping apparatus according to claim 1, 'wherein the circumferentially inner wall of the annular passage is formed by a cylindrical plug while the vortex chamber is defined in the axial direction by one end of the plug and by .a baffle in which the central discharge opening is formed.

3. In a liquid supply system of the type wherein a hydraulic load is fed by a centrifugal pump having the inlet and outlet thereof adjacent the axis and the periphery of the pump chamber, respectively, and an operating speed at which its delivery rate exceeds the upper limit of the range of flow rates over which the demand may vary, so that the liquid flowthrough in the chamber assumes the form of an annulus in the relatively peripheral portion thereof, the relatively axial portion of the chamber being closed to atmosphere so that a hollow core is formed centrally of the liquid annulus to enable it to compensate for variation in the load at a particular demand by adjusting its radial depth: a flow regulating mechanism comprising a source of low pressure liquid which communicates with the pump inlet through a connection having a passage therein for regulating pump inflow, said passage having an orifice opening thereinto, at one peripheral boundary of the inflow, and control means connected to the orifice to discharge a variable amount of additional liquid into the inflow along a tangent thereto, whereby a vortical movement is generated in the inflow and the pressure change therein is variable over a range corresponding to the range of inflow rates needed to satisfy the demand, the pump inflow regulating passage being connected to the pump inlet by a discharge opening which is disposed adjacent the vortical axis of the inflow and characterized with a smaller outside diameter than that of the passage.

4. A liquid supply system according to claim 3 wherein the passage has an annular cross section, and a vortex chamber is interposed between the passage and the discharge opening to collect and feed the inflow through the opening.

5. The liquid supply system according to claim 3, wherein the discharge opening coincides with the pump inlet and is disposed on the rotational axis of the pump adjacent the eye of the pump impeller.

6. The liquid supply system according to claim 3, wherein the control means includes a connection to the delivery of the pump whereby the net delivery of liquid to the hydraulic load is substantially equal to the pump inflow from the low pressure source.

7. The liquid supply system according to claim 6, wherein the control means also includes a flow selector operable to produce a demand signal, a flow-measuring device arranged to produce a signal of pump inflow from the low pressure source, and a valve which is operable to vary the flow of liquid through the orifice, the valve having a movable member which is operated in response to the demand signal, and in response to the pump inflow signal applied in the negative feedback sense.

8. The liquid supply system according to claim 7, wherein the flow-measuring device is disposed in the connection between the low pressure source and the pump inlet.

References Cited UNITED STATES PATENTS 2,306,742 12/ 1942 Moody 103-97 2,336,010 12/1943 Gregory 230-l 14 2,449,002 9/ 1948 Moody 103-97 2,826,147 3/ 1958 Gaubatz 1035 3,004,494 10/ 1961 Corbett 103--97 3,041,848 7/1962 Greenwald 2301 14 ROBERT M. WALKER, Primary Examiner. 

